Measuring instrument.



H. DARWIN. MEASURING INSTRUMENT.

LPPLIOATION FILED APR. 4, 1908. 910,509. Patented Jan. 26, 1909.

2 SHEETS-SHEET 1.

1 Mun J MW, $75M HvDARWIN'.

MEASURING INSTRUMENT. APPLIOATION FILED APR. 4, 1908.

91 0,509. Patnted Jan. 26, 1909.

2 8HEETSSHEET 2.

\ ll-lllll III-IN I J Ill I lwllllllllllllllllllll HORACE DARWIN, OFCAMBRIDGE, ENGLAND.

MEASURING INSTRUMENT.

Specification of Letters Patent.

Patented Jan. 26, 1909.

Application filed April 4, 1908. Serial No. e25,161.

To all whom it may concern:

Be it known that I, HORACE DARWIN, a subject of the King of England,residing at Cambridge, in the county of Qambridge, England, haveinvented certain new and useful Improvements in Measuring Instruments,of which the following is a specification.

This invention relates to measuring instruments of the type in whichmicrometric devices are used for the measurement of linear dimensions orof differences or changes of linear dimensions. ln such instrumentsadjustment of the micrometer has to be made in accordance with thelinear magnitude which is being measured, and one object of thisinvention is to provide ready and accurate meansfor determining theaccuracy of such adjustment.

In a measuring instrument according to this invention a tongue or feeleris employed which can vibrate or be moved to and fro across the axis ofthe micrometer screw, and if the adjustment be correct, the motion isvery slightly opposed by the point of the micrometer screw, which givesrise to a sound if the vibration of the tongue be rapid, or may be feltif the tongue be moved gently by hand.

If the motion of the feeler be found to be entirely unopposed, themicrometer may be judged to be too far withdrawn from the feeler. On theother hand, should the micrometer be too close to the feeler, the motionmay be entirely prevented or considerably opposed.

The invention also comprises improvements in certain details ofconstruction hereinafter referred to, and illustrated in the drawings.

By way of example the invention will be described as applied to anextensometer, that is an instrument for measuring the elongation of agiven length of a piece of material under test under a given load in atesting machine.

In the accompanying drawings, Figure 1 is a perspective view showing anextensometer according to this invention with a portion broken away forthe sake of clearness. Fig. 2 is a central vertical section, Fig. 3 aplan of a portion of the instrument seen from eneath. Fig. 4 is aperspective view of a detail, and Fig. 5 a plan view of a portion ofanother construction of extensometer also according to this invention.

Like letters indicate like parts throughout the drawings.

With reference first to Figs. 1, 2, 3 and 4, A is a test piece havingpivotally engaged with it a member B with forked arms or lugs BEngagement between this member and the test piece A is made through theconical ends of center-points C which engage with punch marks ordepressions made for them in the test piece. The member B is supportedupon a knife edge D forming part of a member D pivotally engaged withthe test piece through center-points D acting in a manner similar tothat described with reference to the center-points C in the member B.This member D is provided with a micrometer screw E working in a nut Fadjustable to take up any wear or backlash which ma occur, and providedwith a graduated head E cooperating with a reading line on a bracket Eattached to the member D.

Mounted on the member B is a tongue or feeler in the. form of a springblade G provided with an edge G preferably of steel so disposed that ifproduced it would intersect the knife edge l). This tongue G can vibratein a plane at right angles to the axis of the micrometer screw E, but ispreferably normally out of alinement with that axis so that any movementof the blade towards the point of the screw is not likely to result ininjury to either of those members.

As will be seen by reference to Fig. 2, the member B does not beardirectly upon the knife edge D but is provided with a plate H which isattached to the member and rests u on the knife edge. This plate His arocking p ate being provided with a ridge H about which it can be rockedslightly by means of adjusting screws; one of these is shown at H inFig. 2, and from the perspective view of the plate shown in Fig. 4 itwill be seen that provision is made for two such screws, one on eachside of the ridge E. This adjustment of the plate H on the member Baffords a delicate means for altering the relative lengths of the armsof the lever formed by the member B and the blade G, and such alterationcan be used for the adjustment of the readings given by the divided headE of the micrometer screw E.

In order that the center-points O and B may be kept in proper alinement,mechanism is provided by means of which each point may be caused to movetowards or away center-points U and l).

fromthe test piece without rotation, thus or 1), but the other stud Kbeing slidable in a hole made to receive it in the member and furnishedwith .a screw portion IQ and milled head K By loosening the milled headK the plate J may be allowed to drop slightly at one side to let thecenter-point slide in its \l-groove, and when that adjustment has beenmade, the tightening of the nut K suffices to clamp the point firmly inplace.

'I he movement of each center-point in its seating is brot ght about bymeans of a screw L which engages with a threaded 11 g L on the member 15or U respectively, and is furnished with a head L having a recess intowhich the end of the center-point enters, and a plate L adapted toengage with a circular recess D in that point. line construction isshown clearly in big. 3 of the drawings, and it will be seen that byrotating the head L of the screw, the center-point b is caused to movelongitudinally in its groove without rotation.

A weight M serves to keep the plate H resting closely upon the knifeedge 1).

'l he method of working with the extensometer described is as follows-1he test piece A is first suitably indented at two pairs of oppositepoints so that the extenscmeter can be attached to it by means of thecenter points 0 and D 'lhe test piece is then placed in a testingmachine, and the extensometer attached to it, the micrometer screw Ebeing so adjusted that on moving the blade or feeler G from side toside, or causing it to vibrate rapidly, the presence of the point of themicrometer screw can only just be detected. A reading of the micrometerhead E is then taken.

A known load is next applied to the test piece uhich is thus caused tostretch. In particular, the extension of that part of the test piece uhich lies between the pairs of center-points C and D causes the edge Gof the blade G and the point of the micrometer screw E to approach oneanother. 'lhe amount of this approach will bear to the extension of thetest piece between the two sets of center-points aforesaid, a ratiodepending upon the proportioning of the parts of the extensometer. Thenext step is to readjust the micrometer screw so that on moving theblade G from side to side or vibrating it as before, the contact betweenthe screw point and the blade is once more only barely perceptible. Themicrometer head is again read and the difierence between the reading nowobtained and that obtained before the application of the load, gives ameasure of the amount of extension of the test piece.

The head may, of course, he graduated to express directly in terms ofsome convenient unit the extension of that portion of the test piecewhich lies between the center-points C and D or any other convenient andusual arrangement may be adopted.

When dealing with thin or flexible test pieces, there is a tendency forthe vibrations of the ieeler G to be transmitted to the whole instrumentand to the test piece. To obviate or lessen this defect, a vibratingieeler having two tongues somewhat after the fashion of a tuning-forkmay be employed. Such a construction is illustrated in plan in Fig. 5,where a second tongue G is shown connected at its root with the tongueG. In such a form of instrument the parts would be so arranged that onlyone tongue, for instance the tongue G, vibrates across the axis of themicrometer screw E, the other being out of range and serving only tovibrate with the first tongue and prevent the undesirable transmissionof the vibrations to the rest of the instrument.

W hat I claim as my invention and desire to secure by Letters latentis- 1. In a measuring instrument the combination of two members adaptedto be engaged with the material under test a point or projection carriedly one member and a i'eeler carried by the other member and adapted tomove in a plane perpendicular to motion of the measuring means toindicate by sound the accuracy of the adjustment.

3. In a measuring instrument the combination of two members adapted 'tobe attached to the material under test a micrometer mounted on one ofsuch members and a flexible tongue or feeler carried by the other memberand adapted to be vibrated transversely to the axis of the micrometer toindicate by contact the accuracy of its adjustment.

4. In a measuring instrument the combination of a member provided withmeans for pivotally engaging the material under test, a knife-edgeforming part of said member, a second member also adapted to be engagedwith the material under test and supported on said knife-edge, amicrometer screw mounted on the first member and a flexible tongue orfeeler mounted on the second member so as to be movable across the axisof the micrometer screw. l t

5. In a measuring instrument the combination of a member, means wherebysaid member may pivotally engage the material under test, V-groovesformed in said member, center-points slidable in said grooves, means forsliding said center-points in the grooves without rotation and means forclamping them in the grooves.

6. In a measuring instrument the combination of a member adapted to bepivotally engaged with the material under test, V- grooves formed insaid member, centerpoints slidable in said grooves, means for slidingsaid center-points in the grooves without rotation, means for clampingthem in the grooves, a knife-edge forming part of such member, a secondmember also provided with center-points adapted to be moved in V-grooveswithout rotation and to be clamped therein, a rocking plate attached tosaid member and forming a bearing for the knife-edge, and means forrocking said plate to adjust slightly the point at which the secondmember is supported on the knife-edge.

7. In a measuring instrument the combination of a member adapted to bepivotally engaged with the material under test, V- grooves formed insaid member, center-points slidable in said grooves, meansfor slidingsaid center-points in the grooves without rotation, means for clampingthem in the grooves, a knife-edge forming part of such member, a secondmember also provided with center-points adapted to be moved in V-grooveswithout rotation and to be clamped therein, a rocking plate attached tosaid member and forming a bearing for the knife-edge, means for rockingsaid plate to adjust slightly the point at which the second member issupported on the knife-edge, a micrometer screw mounted on the firstmember, a flexible tongue or feeler mounted on the second member so asto move across the axis of the micrometer screw to indicate by sound theaccuracy of its adjustment.

8. In a measuring instrument the combination of a member adapted to bepivotally engaged with the material under test, V- grooves formed insaid member, center-points slidable in said grooves, means for slidingsaid center-points in the grooves without rotation, means for clampingthem in the grooves, a knife-edge forming part of such member, a secondmember also provided with center-points adapted to be moved in V-grooveswithout rotation and to be clamped therein, a rocking plate attached tosaid member and forming a bearing for the knife-edge, means for rockingsaid plate to adjust slightly the point at which the second member issupported on the knife-edge,

a micrometer screw mounted on the first member, a flexible feelercomprising two tongues mounted on the second member and so disposed thatone of said tongues can be moved across the axis of the micrometer screwto indicate by sound the accuracy of its adjustment.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses HORACE DARWIN.

Witnesses:

HARRY S. SEIDYL, A. J. FRENCH.

